This invention relates generally to a metallic hose coupling for flexible rubber and plastic hose, and more particularly, to a permanent attached hose coupling which is crimped in place on the end of the hose.
Hose ends of the permanently attached type generally comprise a unitary assembly having a tubular insert member which extends within the bore of the hose and an outer sleeve member extending over the outer surface of the hose for substantially the same length as the insert extends within the hose. Usually, the outer sleeve is a separate piece from the insert, and is permanently secured to the insert by suitable means, such as a mechanical deformation or welding, and the insert extends beyond the sleeve to terminate in a suitable threaded fitted portion.
Two of the most important requirements of a hose fitting are, first, that it provides a seal with the hose so as not to allow the fluid within the hose to leak to the exterior of the assembly, and, second, that it grip the hose with sufficient force against the axial pressure forces exerted when the system is pressurized to prevent physical separation of the fitting and hose. This can be obtained by providing what is known as a "bubble crimp" with a generally thin outer sleeve wall of uniform thickness. In forming such a crimp, the crimping dies are provided with a plurality of annular ridges and grooves which force the outer sleeve into a similar configuration in which the sleeve is deformed inwardly a greater amount at a number of axially spaced points, with reduced deformation intermediate these points.
Other problems that are encountered often result from variations in tolerances not only of the metal hose end, but also of the rubber or plastic tube, which generally has one or more layers of fabric or wire braid interposed between inner and outer layers of rubber or plastic, and in some cases may also be covered by a braided layer of fabric or wire. Generally, such hoses ends are attached to a hose in a machine in which a plurality of collet segments are moved radially inward to deform the metal, and the amount of such deformation is generally fixed by stops within the crimping machine. If, as a result of tolerance variations, the gripping produced by the crimping segments is insufficient, the hose end may permit leakage between the insert and the inner wall of the hose, past the end of the hose and thence toward either past the attachment of the outer sleeve to the insert or along the outer surface between the hose and the sleeve. Also in such case, exposure of the hose to high pressure may cause the hose end to lose its grip on the hose so that the hose end is blown off and separated from the hose. On the other hand, if the deformation produced by the crimping machine is too great, the hose may be physically damaged, particularly by crushing or weakening the braid layers in the hose, as well as by cutting of the rubber or plastic materials, and, as a result, the hose may fail by fatigue as the result of continued flexing or pressure pulsing within the hose.